1. Field of the Invention
This invention relates to data transmission systems and more especially it relates to Asynchronous Transfer Mode (ATM) systems.
2. Description of the Related Art
Data traffic is inherently bursty in nature. This means that the bandwidth required for a data connection measured over the whole duration of a call may be considerably less than the peak bandwidth as measured over a much smaller time interval. The problem for the network is how to efficiently allocate sufficient resource (bandwidth) across the path of a connection without affecting the quality of service provided to other users.
The simplest resource allocation scheme is to reserve a peak bandwidth requirement across the connection path for the whole duration of the call. However, this can be very inefficient for bursty data services as the mean bandwidth requirement may be very much smaller than the peak bandwidth requirement. A scheme has been proposed which can increase the efficiency of resource allocation, namely the Fast Reservation Protocol (FRP) which has been proposed by CNET in France. This scheme calls for an in-call parameter re-negotiation technique to alter the reserved bandwidth during the period of the call. Although the FRP scheme provides many improvements over peak bandwidth allocation for efficient use of network resources, the performance and efficiency can nevertheless be degraded under certain circumstances. Degradation may particularly occur where the peak bit rate of a data burst is large with respect to a link bit rate and additionally degradation may occur where the mean burst duration is comparatively small with respect to the `round trip delay` which is defined by the time required for a data cell to travel from a source to an `egress node` (as hereinafter defined) and back to the source.